WIND TURBINE BLADE WITH TIP END SERRATIONS

Abstract

The present invention relates to a wind turbine blade (10) comprising two or more serrations (100a, 100b, 100c) provided along a section (S) of the trailing edge (20). The section (S) extends spanwise from the tip end (14) towards the root end (16) for up to 5% of the total blade length (L), The serration (100a) closest to the tip end has a height (H) and/or width (W) greater than the respective height (H) and/or width (W) of at least one other serration (100b, 100c) in said section. The present invention also relates to a wind turbine (2) comprising at least one wind turbine blade (10) of the present invention and to a serrated panel (66).

Claims

1. A wind turbine blade (10) having a profiled contour including a pressure side (52) and a suction side (54), and a leading edge (18) and a trailing edge (20) with a chord (60) having a chord length extending therebetween, the wind turbine blade (10) extending in a spanwise direction between a root end (16) and a tip end (14), the wind turbine blade (10) comprising two or more serrations (100a, 100b, 100c) provided along a section (S) of the trailing edge (20), said section (S) extending spanwise from the tip end (14) towards the root end (16) for up to 5% of the total blade length (L), wherein the serration (100a) closest to the tip end has a height (H) and/or width (W) greater than the respective height (H) and/or width (W) of at least one other serration (100b, 100c) in said section.

2. A wind turbine blade according to claim 1, wherein the serration (100a) closest to the tip end (14) has a height (H) and/or width (W) greater than the respective height (H) and/or width (W) of at least two other serrations (100b, 100c) in said section (S).

3. A wind turbine blade according to claim 1, wherein the serration (100a) closest to the tip end (14) has a height (H) and/or width greater than the respective height and/or width of all other serrations in said section (S).

4. A wind turbine blade according to claim 1, wherein the section comprises: a first serration closest to the tip and having a first height and first width, a second serration farther from the tip and having a second height and second width, and a third serration even farther from the tip end and having a third height and third width, wherein the first height is greater than the second height, and wherein the second height is greater than the third height.

5. A wind turbine blade according to claim 1, wherein the height (H) and/or width of the serrations in said section (S) gradually increases towards the tip end (14).

6. A wind turbine blade according to claim 1, wherein the chord length of the blade increases from the tip end (14) towards the root end throughout said section (S).

7. A wind turbine blade according to claim 1, wherein the blade comprises three or more serrations provided along said section (S).

8. A wind turbine blade according to claim 1, wherein one or more of the serrations are arranged at incidence to the flow over the wind turbine blade.

9. A wind turbine blade according to claim 1, wherein one or more of the serrations are arranged at an angle to the chord line of between 1-45 degrees, preferably between 1-25 degrees.

10. A wind turbine blade according to claim 1, wherein the serration (100a) closest to the tip end (14) is arranged at an angle to the chord line of 5-45 degrees.

11. A wind turbine blade according to claim 1, wherein the serrations are arranged substantially coplanar with a trailing edge streamline.

12. A wind turbine blade according to claim 1, wherein the height (H) of each serration corresponds to 10-40% of the chord length of the blade at the midpoint of the base of the serration.

13. A wind turbine blade according to claim 1, wherein the height (H) of the serrations is between 100 and 250 millimeters, and optionally wherein the height (H) of the serration (100a) closest to the tip end is at least 150 millimeters.

14. A wind turbine blade according to claim 1, wherein the tip end (14) further comprises a winglet or tip vane.

15. A wind turbine (2) comprising at least one wind turbine blade (10) as claimed in claim 1.

16. A serrated panel (66) for a wind turbine blade (10), wherein the panel (66) is arranged to be attached to the trailing edge (20) of a blade to form a plurality of serrations at the trailing edge of the blade, wherein the panel comprises two or more serrations (100a, 100b, 100c), wherein the serration (100a) closest to the tip end (14), when the panel is attached to the blade, has a height (H) and/or width (W) greater than the respective height (H) and/or width (W) of at least one other serration of said panel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0033] The invention is explained in detail below with reference to embodiments shown in the drawings, in which

[0034] FIG. 1 shows a wind turbine,

[0035] FIG. 2 shows a schematic view of a wind turbine blade,

[0036] FIG. 3 shows a schematic view of an airfoil profile through section I-I of FIG. 4,

[0037] FIG. 4 shows a schematic view of the wind turbine blade, seen from above and from the side,

[0038] FIG. 5 illustrates a set of trailing edge serrations;

[0039] FIG. 6 shows a schematic view of a wind turbine blade according to the present invention,

[0040] FIG. 7 is a top view of a tip end of a wind turbine blade according to the present invention,

[0041] FIG. 8 is a side view of a tip end of a wind turbine blade according to the present invention, and

[0042] FIG. 9 is a perspective view of a serrated panel according to the present invention.

DETAILED DESCRIPTION

[0043] FIG. 1 illustrates a conventional modern upwind wind turbine according to the so-called

[0044] Danish concept with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8. The rotor has a radius denoted R.

[0045] FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade 10 according to the invention. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

[0046] The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 may be constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance r from the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

[0047] A shoulder 40 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

[0048] It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

[0049] FIGS. 3 and 4 depict parameters which are used to explain the geometry of the wind turbine blade according to the invention.

[0050] FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during usei.e. during rotation of the rotornormally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 or chord line with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centers of these inscribed circles and the deviation or distance from the chord 60 is called the camber f,

[0051] The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

[0052] Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position d.sub.f of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position d.sub.t of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position d.sub.p of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

[0053] FIG. 4 shows other geometric parameters of the blade. The blade has a total blade length L. As shown in FIG. 3, the root end is located at position r=0, and the tip end located at r=L. The shoulder 40 of the blade is located at a position r=L.sub.w, and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. The curvature of the trailing edge of the blade in the transition region may be defined by two parameters, viz. a minimum outer curvature radius r.sub.o and a minimum inner curvature radius r.sub.i which are defined as the minimum curvature radius of the trailing edge, seen from the outside (or behind the trailing edge), and the minimum curvature radius, seen from the inside (or in front of the trailing edge), respectively. Further, the blade is provided with a prebend, which is defined as y which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

[0054] With reference to FIG. 5, an enlarged view of a plurality of common serrations 100 are shown to illustrate some dimensions of the serrations. The serrations 100 comprise a base end 102 which is to be arranged at the trailing edge 20 of the wind turbine blade 10, and an apex 104 which extends downwind of the blade trailing edge 20. A notional line extending from a midpoint of the base 102 to the apex 104 defines a height H of the serration. Also, each serration has a width W of its base. The illustrated serrations are substantially planar, but it will be understood that the serrations may vary in depth or thickness, in particular having tapered or chamfered edges. The serrations 100 are shown as having a profile substantially corresponding to an isosceles triangle, but it will be understood that other serration shape profiles may be used, e.g. curved or wave-shaped profiles, crenelated edges, etc.

[0055] FIG. 6 is a schematic view of a wind turbine blade according to the present invention. The blade 10 comprises three serrations 100a, 100b, 100c provided along a section S of the trailing edge 20. The section S extends spanwise from the tip end 14 towards the root end for 5% of the total blade length L. The serration 100a, which is closest to the tip end, has a height and a width greater than the respective height and width of the two other serrations 100b, 100c in said section S. Also, the height and width of the serrations 100a, 100b, 100c in said section S gradually increases towards the tip end 14.

[0056] A similar embodiment is illustrated in FIGS. 7 and 8. Here, the blade comprises four serrations 100a, 100b, 100c, 100d along a section of the trailing edge 20. The serration 100a, which is closest to the tip end, has a height and a width greater than the respective height and width of the other serrations in said section. Again, the height and width of the serrations 100a, 100b, 100c, 100d in said section gradually increases towards the tip end 14. FIGS. 7 and 8 also illustrated the vortices 64 produced by the tip end 14 of the blade and by the serrations 100a, 100b, 100c, 100d.

[0057] In the embodiment illustrated in FIG. 9, the serrations 100a, 100b are provided as part of a serrated panel 66 for attachment to the trailing edge of a wind turbine blade. The panel 66 comprises a panel base section 68 for attachment to the blade, with the serrations 100a, 100b arranged at an angle to the panel base section 68 such that the serrations 100a, 100b are arranged at incidence to the air flow over the wind turbine blade. The direction of air flow over the wind turbine blade is generally indicated by the arrow F. As seen in FIG. 9, the serration 100a closest to the tip end, when the panel is attached to the blade, has a height greater than the height the other serration 100b of the panel 66.

[0058] The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.

LIST OF REFERENCE NUMERALS

[0059] 2 wind turbine [0060] 4 tower [0061] 6 nacelle [0062] 8 hub [0063] 10 blade [0064] blade tip [0065] 16 blade root [0066] 18 leading edge [0067] 20 trailing edge [0068] 22 pitch axis [0069] 30 root region [0070] 32 transition region [0071] 34 airfoil region [0072] 40 shoulder/position of maximum chord [0073] 50 airfoil profile [0074] 52 pressure side [0075] 54 suction side [0076] 56 leading edge [0077] 58 trailing edge [0078] 60 chord [0079] 62 camber line/median line [0080] 64 vortex [0081] 66 serrated panel [0082] 68 panel base section [0083] 100 serration [0084] 102 serration base [0085] 104 serration apex [0086] c chord length [0087] d.sub.i position of maximum thickness [0088] di.sub.f position of maximum camber [0089] d.sub.p position of maximum pressure side camber [0090] f camber [0091] L blade length [0092] r local radius, radial distance from blade root [0093] t thickness [0094] y prebend [0095] H serration height [0096] W serration width [0097] S section of trailing edge